^^^ what he said. its really not bad, i,ve probably done it a hundred times with my audio install. the top piece where the seatbelt comes out just pops off. dont forget to put the back seat down. also you'll need to pop off the piece where the hatch latches down. 2 little pop clips on that to get access to 1 thats underneath. iirr its about 5-6 of the little pry up clips on the actual piece, plus 2 to get the hatch latch piece off. i dont know if this is getting too basic/detailed, but the clips are 2 concentric circles, use a small screwdriver and pop up the middle circle, it'll pop up a millimeter or two, you can then just pull the cilp out.
once the clips are out, i would just give it a firm tug, grabbing the rear of the piece at the top and bottom, pulling straight out, toward the center of the trunk. there are 2-3 metal clips that will pop out, you'll see them once you've got this part released. now to get it all the way out. give the plastic piece right by the rear door a pull toward the front of the car, giving you some room for your piece to move.
the last part isnt necessarily tricky, but definitely is easier the more youve done it, you kind of hinge -the piece we're trying to get out- into the hatch and lift up a little, the only thing keeping it in at this point is being overlapped by the piece by the rear door and having the seat-back latch through it. hope that wasnt too confusing/ intelligence insulting.